(1)Field of the Invention
The present invention relates to a paper pressing mechanism for paper feeding device, and particularly to a paper pressing mechanism for paper feeding device used in photocopiers having duplex copying function, etc.
(2)Description of the Related Art
In the prior art photocopiers having functions of duplex copying and composition-copying, a sheet having been provided with an image of an original is conveyed onto an intermediate tray (or sheet table) incorporated in the photocopier, and thereafter the sheet once kept on the tray is sent out once more to the copying section.
FIGS. 1 and 2 are schematically illustrative views each showing a photocopier having a different feeding route of sheets of paper. Either of the photocopiers shown in FIGS. 1 and 2 has a publicly known copying unit 50, which comprises an optical unit 51 having a light source, mirrors, lenses and other members combined, an image-formation unit 52 having a photoreceptor drum with an electrifying charger, a transfer charger, etc. disposed therearound, a developing unit 53, as part of the image-formation unit 52, including a developer container, a magnetic roller, etc., and a fixing unit 59 composed of a heat roll, a pressure roll, etc.
Arrows shown in FIGS. 1 and 2 indicate flow of sheets sent out from the fixing unit 54 after passing through the copying unit 50 constructed as above.
Of these, FIG. 1 shows a paper path for duplex copy. Paper with an image fixed thereon in the fixing unit is transferred from the copying unit 50 to a reversing unit 60. In the unit, the sheet is conveyed, as shown by arrow A, through a looping path to an intermediate tray 61 (not shown in detail). FIG. 2 shows a paper path for composition copy, in which sheets are switched back and thereafter passed through a looping path to be reversed and conveyed onto an intermediate tray 61.
FIG. 3 shows a schematically illustrative view showing a paper pressing mechanism for use in the above photocopiers. As is shown in the figure, sheets 63 are piled on the intermediate tray 61. Disposed on the upper side of an exit port 65 adjacent to the intermediate tray 61 in order to covey sheets 63 one by one, is a pick-up roller 75 axially held in a rotatable manner at a free end of a supporting arm 77 which in turn is supported rotatably by an axis 79. A paper pressing arm 71 is attached, to and rotatably together with, the supporting arm 77.
Meanwhile, as sheets 63 are conveyed to the reversing unit 60 as shown in FIG. 1 or FIG. 2, the sheets are bent through the heat roller in the fixing portion, and/or the conveying path, or curled due to hygroscopic property of the sheets, therefore the piled sheets 63 are curled up. To deal with this, the exit port 65 from the intermediate tray 61 must be designed to be higher than the height of the curl, requiring a rather large space. Even if a spacious exit port is formed, when a sheet is sent out to the exit port 65 while remaining in curl, there is still left a fear that paper jam might occur.
Description will be continued of the operation of the paper pressing mechanism shown in FIG. 3 with reference to FIGS. 4(A) and 4(B). Also in FIG. 4(A), a pick-up roller 75, is rotatably held, like what was shown in FIG. 3, at a free end of a supporting arm 77 which in turn is supported rotatably by an axis 79. A paper pressing arm 71 is attached to, and rotatable together with, the supporting arm 77. A paper pressing portion 72 at a distal end of the paper pressing arm 71 is disposed so as to be brought into contact with the sheet 63 at the same time the pick-up roller 75 comes in contact when the supporting arm 77 is rotated from a retracted position to a position where paper is pressed (FIG. 4(B)).
However, making the paper pressing portion 72 and the pick-up roller 75 abut on the sheet 63 substantially at the same instant, demands high precision of the relative position between the both, requiring troublesome labors in manufacturing and assembling.
On the other hand, Japanese Patent Publication Sho 61 No. 54691 discloses a feeding device which can perform a good re-feeding of paper stored in an intermediate paper tray by means of a paper pressing member which presses the sheets f rom the above against the tray so as to prevent the piled sheets on the intermediate tray from coming up, while guiding the sheet to a position between pair rollers upon re-feeding. This method, however, also exhibits insufficiency to prevent the sheets in pile from being fed at once, upon re-feeding of the sheets in curl, so the measure is not complete.